This invention relates to the field of intravascular medical devices and more particularly to balloon dilatation and stent delivery catheters which are readily trackable within vasculature in which they are used.
Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve the use of a balloon catheter with a guidewire, possibly in combination with other intravascular devices such as stents. A typical balloon catheter has an elongate shaft with a balloon attached proximate the distal end and a manifold attached to the proximal end. In use, the balloon catheter is advanced over the guidewire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
There are three basic types of intravascular catheters for use in such procedures, including fixed-wire (FW) catheters, over-the-wire (OTW) catheters and single-operator-exchange (SOE) catheters. The general construction and use of FW, OTW and SOE catheters are all well known in the art. An example of an OTW catheter may be found in commonly assigned U.S. Pat. No. 5,047,045 to Arney et al. An example of an SOE balloon catheter is disclosed in commonly assigned U.S. Pat. No. 5,156,594 to Keith.
Several characteristics that are important in intravascular catheters include pushability, trackability and crossability. Pushability refers to the ability to transmit force from the proximal end of the catheter to the distal end of the catheter. Trackability refers to the ability to navigate tortuous vasculature. Crossability refers to the ability to navigate the balloon catheter across narrow restrictions in the vasculature, such as stenosed vessels or fully and partially deployed stents.
To maximize pushability, some prior art catheters incorporate a stainless steel outer tube (also referred to as a hypotube) on the proximal shaft section and a polymeric distal shaft section. One limitation of such a construction is that hypotubing is often prone to kinking. To reduce the likelihood of kinking, some prior art catheters use a relatively stiff polymer (e.g., composite) or reinforced polymer in the proximal shaft section.
The trackability of a particular catheter design is analyzed in terms of the trackability of the distal portion of the catheter, as this portion must track the guidewire through small tortuous vessels to reach the area to be treated. A more flexible distal portion has been found to improve trackability. Therefore, to maximize pushability, the catheter should have a relatively stiff proximal section. To maximize trackability, the catheter should have a relatively flexible distal section. To maximize crossability, in addition to the characteristics needed for pushability and trackability, the catheter should have a distal tip, the location of which within the vessel can be readily determined so that the progress of the catheter through the vessel can be followed.
One limitation of the basic structure of catheters described above is that kinking can occur at the joint between the relatively stiff proximal shaft section and the relatively flexible distal shaft section. To reduce the likelihood of kinking, some prior art catheters use one or more tubular sections of intermediate flexibility between the relatively stiff proximal section and the relatively flexible distal section to provide a more gradual transition in flexibility theretween. While this approach provides some benefit, the resulting transition in flexibility is often step-wise, and can still be susceptible to kinking at the junctions of the various intermediate sections. In order to overcome this deficiency, an intravascular catheter that has a more gradual transition in flexibility along its length has been needed. A catheter satisfying this need is described in commonly assigned U.S. Pat. No. 5,891,110 to Larson et al., which is incorporated herein by reference.
However, while overcoming some of the problems with regard to flexibility, comparatively little effort has been directed toward facilitating control of the direction of the catheter tip with respect to a deployed stent or a stenosis. Recrossing a deployed self-expanding or balloon-expandable stent with a post-dilation balloon catheter or additional stent delivery catheter, for example, can prove to be a difficult procedure. Inability of the catheter to cross the stent might be due to failing to direct the distal tip of the catheter into the stent lumen. Instead, the distal tip could be directed into the vessel wall or could get hung up in the struts of the stent. It is also possible for the guidewire to be misdirected by threading it between the stent and the wall of the vessel instead of through the stent lumen. The end result would be that the balloon catheter would get stuck in the vessel and could not be easily removed.
Previous attempts to provide catheters that are more readily visualized within the vessel have involved the utilization of radiopaque markers in catheters. For example, it has been proposed to track the balloon of a balloon catheter by placing radiopaque bands inside the balloon. Such bands, however, are of little assistance in positioning the distal-most end of the catheter tip, which may be separated from the balloon by a distance of several centimeters.
It would be desirable, therefore, to provide a catheter having improved crossability. It would also be desirable to provide a catheter in which the precise position of the distal tip relative to a deployed balloon, stent or stenosis could be readily ascertained.
The present invention overcomes many of the disadvantages of the prior art by providing a balloon catheter having a distal tip which can be readily located and its position closely followed within vasculature in which it is deployed. The balloon catheter of the present invention is rendered radiopaque proximate the distal-most tip thereof, enabling the physician to observe the position of the tip of the catheter within the body of the patient. Precise placement of the catheter tip by the physician is thereby facilitated.
Radiopacity can be imparted proximate the distal-most tip of the catheter in any of various ways. These include, among others, (1) embedding the catheter tip with radiopaque powder or particles, (2) applying a radiopaque pigment, such as a paint or ink, to the surface of the tip of the catheter, (3) using a radiopaque contrast media to coat the interior surface of a balloon immediately adjacent the distal-most end of the catheter tip, (4) providing bands of radiopaque material proximate the distal-most end of the catheter tip, (5) providing a coil of radiopaque material encircling the distal-most end of the catheter tip, (6) covering at least part of the catheter tip adjacent the distal-most end thereof with a radiopaque mesh or braid, (7) incorporating radiopaque wires in the wall of at least part of the catheter tip adjacent the distal-most end thereof, (8) capping the distal-most end of the catheter tip with a radiopaque cap, and (9) using an arc of a radiopaque hypotube or similar tubing to encircle at least that part of the catheter tip adjacent the distal-most end thereof. Other ways of imparting radiopacity to at least that part of the catheter tip adjacent or proximate the distal-most end thereof are within the scope of the present invention.
Rendering the catheter tip radiopaque proximate its distal-most end is especially important in balloon catheters, because guiding the catheter tip within stenosed vasculature and particularly through stents deployed therein requires knowledge of the precise position of the catheter tip. A radiopaque catheter tip of the present invention can be viewed within body vasculature from outside the body to enable precise maneuvering and placement of the catheter with respect to the stenosed area or to facilitate passage through deployed stents and the like.